1. Field of the Invention
The present invention is directed to the field of precompression pumps. More particularly, the present invention is directed to a precompression pump used for dispensing, e.g., personal care products, from a container or bottle upon which the pump is mounted.
2. Description of the Related Art
Precompression pumps are known in the art. A precompression pump is a pump in which the outlet valve for the pump chamber opens in response to a predetermined pressure level within the pump chamber. Often, this is accomplished by providing an outlet valve having a surface upon which pressure in the pump chamber acts, and which is biased in a way that the outlet valve only opens when the pressure in the pump chamber is of a sufficiently high level. This type of pump is particularly useful for dispensing personal care products in a fine mist without dribbling.
A problem can arise in precompression pumps of the type described above during priming of the pump. When the pump chamber is in an unprimed condition--i.e., is filled with air instead of the liquid to be dispensed--it is necessary to evacuate air from the pump chamber in order to draw the liquid to be dispensed into the pump chamber. However, the air in the pump chamber can act as a compressible fluid. As a result, in certain precompression pump designs air in the pump chamber is compressed during the downstroke of the pump piston, and the pressure in the pump chamber does not achieve a sufficiently high level to open the outlet valve and release the air in the pump chamber through the pump nozzle. It is therefore difficult to evacuate the air from the pump chamber and to draw liquid into the pump chamber for dispensing. The result is that an undesirable number of "strokes to prime" may be necessary to operate the pump, if the air is not released from the pump chamber in some way other than through opening of the outlet valve.
Several patents describe mechanisms for assisting in the evacuation of air from a pump chamber to allow the pump to be primed. U.S. Pat. Nos. 3,746,260; 3,774,849; 4,051,983 and 4,144,987 show various mechanisms used to evacuate air from the pump chamber of a precompression pump. However, many of these mechanisms are unsatisfactory in that they can vary the volume of the dose, can cause wear or fatigue in the operating parts of the pump, or are difficult to mold. U.S. Pat. No. 5,192,006 shows a pump which includes a feature for evacuating air from the pump chamber. This pump, however, uses friction-operated inlet and outlet valves which can be disadvantageous for several reasons. First, in order for the friction-operated valves to operate properly, several parts must be closely toleranced to ensure proper frictional fits. In addition, the functional characteristics of the pump can vary depending on variations in the frictional fit between parts. Furthermore, any variations in tolerancing can result in frictional fits which can prevent the valves from opening and/or can cause the valves to remain open when they are intended to be closed. Finally, the design of the parts necessary to achieve the frictional fits involves detailed, and potentially expensive, molding equipment.